Infra-red radiant panel heater using PTC conductive polymeric electrodes

ABSTRACT

An infrared radiant panel heater utilizing a liquid-tight enclosure with at least one surface emissive of infrared energy by liquid inside the enclosure. A pair of polymeric electrodes having the property of positive temperature cut off are submerged in the liquid inside the enclosure, near the bottom thereof. Liquid is heated by electrical current flowing through the liquid between the electrodes. Convective flow of liquid distributes heated liquid throughout the enclosure. The cutoff temperature can be selected by electrolyte concentration in the liquid (usually water and sodium chloride) and the properties of the electrodes. In some embodiments a reversed face of the enclosure is reflective, so that most of the infrared energy is directed into the room rather than against a wall.

FIELD OF THE INVENTION

A radiant panel heater which heats a room by way of two spaced apart water-immersed electrodes contained in an enclosure that is designed to heat the water and radiate long infrared wavelengths for heating a space such as a room. The water is joule-heated by electrical current flowing through it between the electrodes. The electrodes are made of polymeric material, which has the property of positive temperature coefficient to prevent overheating of the heater, establishment of the temperature to which the water is heated.

BACKGROUND OF THE INVENTION

This invention relates to heaters of the type (usually panels) which heat a room by way of long infrared waves, rather than by forced air flowing through super-hot heating elements, or by convection as in oil-filled or water-filled radiator-style heaters. With this invention, a room is heated by radiation from a warm surface that has been coated or treated with an appropriate texture well known by one versed in the art of infrared heat transfer. The texture is designed to emit long infrared wavelengths when heated from within by a body of liquid that has been joule heated when placed between two electrically conductive PPTC (polymeric positive temperature coefficient) electrodes. The construction of which will be clear and appreciated in the drawings and detailed description.

There exist two basic types of portable and surface-mounted auxiliary heating devices used for heating a room. These include forced air heating types and radiant heating types. Of the radiant heating type, there exist subsets. These subsets include high temperature types that glow red-hot such as filament wires and gas-heated structures, both of which utilize reflective surfaces to reflect and direct the infrared energy. Another type is the radiant energy heater that utilizes a large, flat area, the face of which could range from an entire floor to panels that can be placed under a working desk to keep legs and feet warm. Their surface temperatures rarely exceed 83 degrees C. (180 degrees F.). Such flat panel radiant heaters are the subject of this invention.

So called “radiant” panel heaters differ from conventional hot wire element space heaters by their lack of a motor that turns a fan to push air through them. Instead of heating the air in a room, radiant space heaters deliver long waves of infrared energy, heating the surfaces of objects in the room, which in turn radiate back into the room. Such heaters find their most common usage in northern Europe, Asia and other parts of the world where economy is valued and space is limited. They are gaining much popularity in the United States.

Among their advantages is that they can be mounted directly onto a wall, relieving floor space that conventional space heaters would otherwise occupy. Their surfaces need not exceed a temperature of 82 degrees C. (180 degrees F.) To take advantage of the long infrared wavelengths, objects and persons in a room subject to line of sight of a radiant panel heater absorb the warmth from its surface while the air in the room maintains its subjectively cooler ambient temperature. The economies of which will become apparent in the detailed description of the invention.

A further advantage is that the instantly transmitted radiant energy does not pass through glass. Therefore windows consequently pose no heat loss.

There exist disadvantages of existing radiant panel heaters in that they suffer from unevenly heated surfaces due to the juxtaposition of imbedded heating wires placed between their front and rear panels, essentially reducing the purpose of the efficiency of emitting uniform long infrared waves over a large area.

Another disadvantage of radiant panel heaters is their slow warm-up. Because they are resistance wire heated, they exhibit a fixed current draw in relation to their mass, and heat slowly until they reach the dissipation equilibrium temperature of power-to-heat sinking.

It is yet another disadvantage of existing radiant panel heaters that when mounted in their typical vertical fashion, their upper portions tend to be much hotter than their lower portions.

It is another disadvantage of existing radiant panel heaters that mount either to a wall or to a ceiling that their radiant energy emits from both sides, namely the side facing into a room and the another side facing a wall. This consequently transfers 50% of their energy directly into the wall they are mounted to.

It is yet another disadvantage of existing radiant panel heaters that their basic construction does not readily lend itself to high volume manufacturing techniques. Typically extruded aluminum frames are employed, and flat panels are cut from standard sheets and screwed or riveted together. Heating elements can be of printed circuit board materials or sheathed heating elements that are bent or formed into shape, and so on. It is accepted as of this writing that the cost of a conventional radiant panel heater can be from double to 3 times the cost of a comparable wattage fan or blower type forced air space heater.

It is an object of this invention to provide a flat panel radiant heater whose cost is much less than existing flat panel radiant heaters by employing a design that takes advantage of the types of constituent parts which can be made with known high-volume production techniques and methods. Such parts include injection molded, high production stampings, and processes used by inflatable toy manufacturers.

It is another object of this invention to provide a panel radiant heater that heats quickly by joule heating of water contained within a gland (preferably a resilient gland) resembling a small, thin swimming pool floatation raft. The uniform heating is a product of circulating water due to convection currents within a thin gland made from a material such as polyvinyl chloride (PVC). The result of this is rapid and even heat distribution due to reduced mass, and thin material cross sections.

It is yet another object of the invention to provide a panel radiant heater which has no resistance-type heating elements and consequently constitutes no risk of fire.

It is another object of the invention to provide a panel radiant heater in which the hottest component of the heater is the water contained therein.

It is yet another object of the invention that the maximum heat generated internally and externally can never exceed institutional limitations such as imposed by UL, CSA, CBR and others. In practice it is thermally safe to humans, and in particularly is safe to child contact.

It is another object of the invention to safely limit the current draw of the panel radiant heater by way of polymeric positive temperature coefficient conductive plastic electrodes that regulate and limit current draw by decreasing or eliminating their conductivity as a function of increased temperature.

It is another object of the invention to limit the water to a predetermined temperature by utilizing the merits of a polymeric positive temperature coefficient conductive material, whereby said material becomes non-conductive at a temperature that is pre-settable by the selection of the polymeric density of the crystalline resin and conductive particles used therein. The molecular weight of these is well known by persons versed in the art of producing positive temperature coefficient polymers.

It is yet another object of the invention to provide a panel type radiant heater that cannot burn out and which has an indefinite life expectancy.

It is yet another object of the invention to provide a panel type radiant heater that can accommodate any available voltage throughout the world with no change of configuration in any of its constituent parts other than a line cord plug change and a matching water conductivity.

It is yet another object of the invention to utilize water contained within a gland that is mixed to a predetermined water conductivity by adding an electrolyte, preferably adjusting its conductivity to obtain a specific wattage draw to any given voltage by adjusting the concentration of electrolyte.

It is another object of the invention to provide a flat panel radiant heater that utilizes water as its resistive medium to be joule heated by way of PPTC electrodes in which no corrosive action or electrolytic corrosion occurs. No metal comes into contact with the conductive water.

It is yet another object of the invention to utilize the joule heating properties of the conductive water in conjunction with the internal resistance self-heating properties of the electrode material to provide an added feature of regulation for current. These two individual aspects of heating PPTC materials to their trip point have never been utilized respectively in conjunction with each other, to the knowledge of the inventor herein.

It is an additional object of the invention to radiate nearly 100% of the radiant energy from the side of the panel that faces into a room while emitting and radiating almost none of its energy into the wall or ceiling to which it is mounted.

BRIEF DESCRIPTION OF THE INVENTION

A panel type radiant heater according to this invention comprises an enclosure that is filled with water of specific conductivity that is joule heated by way of a pair of spaced-apart polymeric positive temperature coefficient (PPTC) conductive plastic electrodes mounted therein. The enclosure is contained by, or supported by structural support. Thermal transfer from the enclosure is provided to a side surface that is specifically prepared with an infrared-emitting textured surface that faces a region to be heated, such as a room. Preferably the rear side panel is specifically prepared with a surface that does not emit infrared that faces the wall onto which it may be mounted. This is called the wall-mounted embodiment.

An optional embodiment of the invention called the freestanding unit comprises the component of the said wall-mounted embodiment, but has both of its outer surfaces specifically prepared with an infrared-emitting texture surface. As its name implies, it utilizes a support base onto which the free-standing unit is placed, said base being designed for resting on a floor or substantial support surface, and movable to any suitable location where heating is desired in two or more directions.

The pair of spaced-apart conductive plastic electrodes is mounted in the enclosure so arranged that an appropriate volume of conductive water is disposed between them so as to be joule heated by current that flows through the water from one electrode to the other.

The above and other features of this invention will be fully understood from the detailed description and the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a first PPTC electrode with an insert molded contact pin.

FIG. 2 is an isometric exploded view of a first and second PPTC electrode with its two taper lock spacers.

FIG. 3A is an isometric exploded view of an assembled PPTC electrode module.

FIG. 3B is a profile drawing of one taper lock spacer showing the locking tapered surfaces.

FIG. 3C is a section view showing a taper lock spacer disposed between two PPTC electrodes.

FIG. 4A is an isometric drawing of a gland assembly showing the PPTC electrode module in hidden lines within.

FIG. 4B is a section view of a gland assembly showing the PPTC electrode module within and illustrating the glands front to back attachment points and water pathway in between.

FIG. 5A is a cutaway portion of the gland assembly that has been turned upside down illustrating the inlet nozzle for filling with water of a predetermined conductivity.

FIG. 5B shows the same cutaway portion at the gland assembly turned right side up and more clearly illustrating the attachment points between the front and rear resilient layers of the gland and water pathway. It also shows the inlet nozzle with its integral plug in place for water containment.

FIG. 6A is an isometric exploded view drawing of the entire radiant heater assembly showing its integral parts and in particular its rear surface which is designed to emit little or no radiation energy.

FIG. 6B is an isometric exploded view drawing showing the radiant heater's three main components, and in particular its front surface which is designed such as to emit radiant energy off its surface.

FIG. 7 is a schematic drawing of the gland's water convection flow throughout its pathways.

FIG. 8 is a cross section of the radiant heater as mounted to a wall or ceiling, illustrating its directional ability to radiate long wave infrared energy toward the center of a room while its rear surface utilizes convection to heat air from its rear surface.

FIG. 9 is an isometric drawing of a free-standing floor unit that radiates infrared energy in two directions.

DETAILED DESCRIPTION OF THE INVENTION

Although this invention contemplates temperature regulation and selection of temperatures to be produced, the principal advantages of this invention are derived from the unique application of electrodes that exhibit their own special PTC properties.

According to this invention, the conductive plastic electrodes are principally formed of, and their exposed surfaces are specifically made of, an electrically conductive polymeric resin that exhibits a positive temperature coefficient. The polymer electrode can be loaded with graphite or graphite nodules, carbon black, lamp black, carbon fibers, exfoliated graphite, fibrils or nano-fibers to reduce the bulk electrical resistance of the material and provide suitable conductivity for the electrodes. The preferred polymer for the electrode is polyethylene, and more preferably low density polyethylene although crystalline polymers of one or more olefins and polymers of at least one monomer such as polyvinylidine fluoride and ethylene tetrafluoroethylene and blends of two or more such crystalline polymers are suitable.

The conductive plastic electrodes are formed and their exposed surfaces are specifically formulated to exhibit a positive temperature coefficient (PTC). Experimentation by the inventor herein has taught that electrodes made from a conductive polymer that does not exhibit PTC will not serve, since over time, the water solution's conductivity will increase. This period ranges from at least 24 hours and at most 7 days of continuous operation. The reason for this event is not clearly known. It simply occurs and must be recognized. It will occur, but the length of time required is uncertain. Meanwhile the system must be able to function properly. It would be economically unfeasible to operate each radiant heater, or for that matter, electrode sets, until stabilization occurs, therefore, the need for regulation of temperature by the electrodes from the start is a necessary and important low-cost solution.

This invention makes practical use of two forms of heat exerted on the PPTC electrodes. The first form, and the best known is electrical current that heats the material by way of its own electrical resistance. Those versed in the art of PPTC materials are well aware that such a material exhibits a PTC effect and becomes nearly non-conductive at the material's elevated phase change temperature when an electrical load nearing the load-bearing capacity of the material is reached.

A most common use for PPTC material in this respect is self-resetting fuses for circuit protection. It is not, however, widely known that when PPTC materials are submersed in water, the water will joule heat and as a consequence, it will back heat the PPTC material to its trip temperature. This is, of course, provided that the mix of polymer is below the boiling point of water and the water's conductivity will enable the flow of high enough current. Therefore, the second form of heat exerted on the PPTC electrodes is back-heat from the water which the electrical current between the electrodes caused to occur. The invention takes advantage of both of these two forms of heating to regulate water temperature in a new and novel way.

Should the current passing through a piece of PPTC structure exceed the dissipation rate of said piece of material in air, it will heat, reach the trip temperature and greatly diminish its current draw, or possibly even shut it off. However, back-heating a set of PPTC electrodes when submersed in water is more complex and becomes a system phenomenon. First, there are two structures. Second, they are both submersed in water, which is an excellent heat sink. Therefore, considerably more current can pass through a set of electrodes of the same cross-section when submersed in water. For electrically heating to the PPTC material to its trip point temperature, enough power must pass through the material to both overcome the inherent natural electrical resistance of the material in air, while overcoming the heat sinking effect of the water. However, it is the water's conductivity that drives the current draw on the electrode assembly. In addition, the important factor of the system's heat dissipation plays its most important role as to whether the material will trip internally, or trip from being back-heated by the water itself.

For example, should a small amount of current be applied to a set of electrodes that are placed in a bucket of water, and that water has a median conductivity of about 40 mS, the water temperature may never reach the PPTC material's trip point. We can surmise that this is due to the heat dissipation rate of the bucket and the amount of water being heated. If, on the other hand, the same electrodes are placed in a very well-insulated container, the heat rise will exceed the dissipation rate of the container, and the water temperature will continue to rise even with very low flow of electrical current. When the water reaches the trip temperature of the PPTC material, then, the PPTC material will trip from the back-heat and the resulting regulation of temperature will ensure the same water temperature as through the electrodes were internally heated.

Also in accordance with the invention, it is known that a highly reflective surface will reflect long wave infrared energy or heat. It is not as widely recognized that a highly reflective surface does not emit its own heat as radiated infrared energy, but rather as emission of heat will result from the principle of convection of heat transfer. A perfectly shiny surface can neither absorb nor emit radiation. This fact is a consequence of the Second Law of Thermodynamics, one simple form of which says that heat, of itself, cannot flow from a cold to a hot object. An important related fact is that a perfect absorber of heat is a black body, and consequently the most efficient possible emitter.

At the opposite end of this spectrum is the perfectly shiny body that cannot emit its heat through radiation. An infrared thermometer cannot take a temperature measurement of a mirror, but can measure the temperature of an object reflected off its surface. While important to this invention, it is unnecessary to understand these circumstances—only to know that they exist.

In practice, this invention takes advantage of the black body principle, its surface facing inwardly into a room, and as the consequence of a shiny surface on the side facing a wall, an adjacent wall need not be heated by radiation. Hence, a greater percentage of the output energy of the device is emitted in a useful and more efficient direction.

Through experimentation the applicant has learned that almost any rough or textured, non-shiny/non-reflective surface is suitable for excellent radiation. The textured surface to be used in this invention is not predicated on any color, and therefore can be painted or silk screened with artwork of any kind. The shiny, wall-facing side of the heater can be shinily pre-plated. As other examples, steel or gold iridite (sometimes referred to as Alodine or Chemcoat) can be used when the rear panel is made from aluminum, provided the surface is reflective.

A degree of heat is directly dissipated off a reflective rear panel by way of convection of air along it. The heat rises and provides some warm air circulation within a room, while the wall directly behind the heater absorbs little to no energy.

Referring to FIG. 1, a basic PPTC electrode is illustrated. Electrode 1 comprises a melt-formed shape 10, a contact post 2 and a contact 3 made of any metal. It is preferred that the metal be nickel plated to reduce any oxidation between it and the polymer. Copper, brass or any other non-ferrous metal is not suited for a long-term, molded in, electrical contact with conductive polymers. Slots 5, 7, prepared to accept tapered locking spacers 9 shown in FIG. 2, are disposed, one inserted in from one end and one inserted in from the other end. Said slots 5, 7 have a miter angle 14, and matching the taper 12 shown in FIG. 3B of said tapered locking spacer 9.

In FIG. 3C, electrodes 10 are slidably assembled over said tapered locking spacers 9 with a slight interference fit over said miter angle 14. The result of this is a low-cost, tightly fitted electrode assembly 13 of FIG. 3A exhibiting zero wobble without the use of conventional fasteners.

Referring two FIG. 4A, a gland 15 made of two sheets 17A and 17B of polymeric film, for example for polyvinyl chloride of a thickness at least 020″ (0.5 mm) with a said electrode assembly 13 placed inside and in between sheets 17A and 17B. This film is resilient enough to deform to accommodate itself to a confined region to be described below.

The electrode assembly's contact post 2 protrudes through a molded-on tube fitting 23, said tube fittings 23 having a tolerance fit over the posts of said electrode 10 so that a water-tight seal is made at the joint interface. The tubes of said molded-on tube fittings 23 sufficiently long to allow contact 3 of electrode assembly 13 to be easily accessed for soldering.

Referring to FIG. 4B, the two sheets 17A and 17B of the resilient gland are joined around their entire periphery and at the intervals shown. This makes a fluid-tight enclosure. A network of passageways (channels) 25 is formed in between the attachment points. Passageways above electrode assembly 13 are used as heat dispersion passages. A cool return passage 27 will be further described in FIG. 7.

In FIG. 5A resilient gland 15 is shown in a partial cut away view illustrating only its inlet nozzle 21 and electrode post 3, upside down so that it can be filled 29 with water of a specific electrical conductivity. It also shows the attachment join lines 17C in more visible detail.

The specific conductivity of the water to be used is arrived at by placing electrode assembly 13 (as illustrated in FIG. 4A) that has a specific line voltage attached to its two contacts and submerged. The line voltage for example in the United States is 120 VAC and for Europe is 220 VAC. When electrical power is applied to the electrode assembly in distilled water, no current will be drawn. Adding small amounts of table salt (sodium chloride) in small amounts will increase the conductivity. The water's conductivity can be measured with a number of commercially available water conductivity meters. Such a meter and others are available from Hanna Instruments, Laboratory Division model number H18733.

The radiant panel heater's presently designed size for home use is 20.8 inches high by 27.8 inches wide. This surface area will dissipate approximately 350 to 450 watts at a surface temperature of approximately 175 to 180 degrees F. The invention is not limited to this or any other size. The thermodynamics and heat dissipation formulas for power requirements in relation to product surface area are well understood and can be applied to scale the size of the heater for different outputs.

To ascertain the water's conductivity, an amp meter is attached to the line, and salt is added to the distilled water until an amp meter ready matches and intended value, for example, 450 watts for a line voltage of 120 VAC or 3.75 amps. Measurement of the water's conductivity is in micro siemens per centimeter which is equivalent to micromhos per centimeter at 3.75 amps. The water conductivity is the result of a) the surface conductivity of the electrode assembly, b) the surface area of the opposed faces of the electrode pair and c) the distance between their faces. If for example, the surface conductivity is approximately 28 ohms per square cm., distance between the electrodes is approximately 0.125″ and the area of opposed faces is 12 square inches, then one could expect the water conductivity to be around 185 mS to 200 mS (micro siemens) at 3.75 amps. It will be observed that to accommodate any line voltage for varying countries, the water conductivity and a corresponding line cord plug 45A is all that needs to be changed. This can be done by providing an appropriate amount of electrolyte.

FIG. 5B is the same section of gland 5 as in FIG. 5A, but rotated right side up. After filling and prior to turning gland 15 right side up, water inlet nozzle 21 is closed. FIG. 5B further shows the water passages 25 and their attachment lines 17C. Gland 15 is ready to accept soldering of wires onto the electrode's said contact post 3.

FIG. 6A is an isomeric drawing that shows the radiant heater's constituent parts. Gland assembly 15 is located between a front metal panel 35 and a rear metal panel 36. Panels 35, 36 are designed such that one fits inside the other. Front panel's folded edge fits over the outside of rear panel's folded edge, thereby forming an overlapping joint. Permanently joining the two parts at this joint can be done in a number of ways. One way would be to staple at spaced intervals, another may be to provide tabs on said front panel 35 that are folded over the rear face of rear panel 36. Any of a various number of methods, which are known to one versed in sheet metal fabrication, can be used.

When gland assembly 15 is filled with water, it would pouches apart where the said electrodes are spaced apart. This is due to the lack of attachment lines 17C (FIG. 5B) in that area. Therefore a retaining plate 39 is used to retain the said gland 15 from protruding through the rectangular hole 38 provided in rear panel 36.

An electrical power cord 45A, which incorporates an on/off switch 45B is attached to gland's 15 electrode contact 3 by soldering. Other mechanical-type electrical connections such as a threaded lug or ring terminal can be used instead. A plastic insulating cover 41 with an appropriate line cord strain relief molded into its geometry is attached by sheet metal screw 43. Molded-in power cord strain reliefs are common. One versed in the art of small appliance will be familiar with many optional techniques that could instead be used. The radiant heater assembly is provided with mounting spacers 37 and appropriate wall mounting screws 33 and a cosmetic cap 31 to improve the appearance of the exposed screw head. The appropriate screws 33 can be any high helix screws such as wood screws used for mounting the assembly to a wall or ceiling. Often plastic plugs or some other holding device will be used in a wall's drilled mounting hole to reinforce the mounting. Optional methods are commonly known.

Face 47 of said rear panel 36 is either pre-chrome steel, polished stainless or a shiny, reflective aluminum. Its reflective surface neither radiates heat, nor does it transfer its heat into the surface of the opposed wall that it is mounted to. This is an integral but important feature of the invention. The terms “face” and “surface” are sometimes used interchangeably.

FIG. 6B shows front panel 35 and its face 49. Face 49 is coated with a paint or some other finish that has a texture equivalent to a semi-gloss or texture painted surface. Surface 49 need not be textured per se as much as it needs to be non-reflective. Pertaining to this feature of the invention, the surface can be painted, silk screened uniformly, printed, or imprinted with various images of any color, color being in and of itself having no bearing on infrared radiation. A consequence of this feature of the invention is that the radiant energy that is not emitted from rear panel surface 47, is instead emitted from the surface of front panel 49. Therefore, the greater proportion of energy or wattage therein is mostly emitted from front surface 49. The result is increased efficiency relating to the comfort level of persons in a room.

As a further consequence of the described thermodynamics, a comparison of two identical wattage systems, one being the system of the invention and the other being of the existing state of the art, the surface temperature of the front surface 49 of the invention will be hotter. Therefore, the value in measurable usable performance of the invention equates to less wattage used in obtaining an equivalent surface temperature of face 49 of a radiant panel heater that faces inwardly into a room. The increased performance of the invention over the prior art is mostly equal to the amount of radiation that is not imposed into the wall to which the heater is mounted. The invention takes the energy prior art imposes into a wall and instead redirects it into the room.

Referring to FIG. 7, gland 15 is shown with its water flow line 53 showing the pattern in which the water flows within the said pathways 25 of the gland. The circuitous, but continues pathway 25 contributes to the uniformity of heat throughout. The water in pathways 25 above the electrode assembly 13 transfers heat from inside gland 15 to panel 35, 36 by way of surface contact. Surface convection of said panels 35, 36 removes the heat from the water and cooler water flows downwardly to the electrodes to be re-heated.

Although initial surface temperature of front panel 35 is established by the properly proportioned solution of distilled water and salt, final regulation of the temperature is accomplished by the electrode assembly's positive temperature coefficient polymeric composition.

PCT regulation is necessary to preclude an increase of water conductivity over time. Although it is speculative, it appears that carbon in some form is released into the water over a period of time, and as a result the water's conductivity will increase, and an increased flow of electrical current between the electrodes would be possible. In fact, for whatever reason causes it, it is an observer phenomenon. To maintain a constant and acceptable temperature, the material of electrode assembly 13 is formulated to become non-conductive or near non-conductive at around, but not limited to 83 degrees C. (180 degrees F.). Without a PPTC material for the electrodes, a radiant heater of the invention would initially draw 450 watts. Several days later the draw could increase to 550 or even 800 watts.

A feature of the PPTC material of the invention is that over time, a slow but steady decrease in its bulk conductivity will ensue. It will not be enough to completely offset the increase of the water conductivity in which it is immersed, but still should some failure occur within the material, a PPTC conductive material will always fail to safe.

In FIG. 8, a wall-mounted version radiant heater of the invention is mounted and spaced away from a wall by four said spacers 37. Radiant energy 55 is mostly radiated from its said front face 49 into, and toward the middle of a room, whereas there is little radiant energy emitted from its rear face 47 imposing little heat into its mounting surface 57. There exists, however, some air convection in the form of some surface heat transfer to the air, which rises 56 from the bottom of the heater and exits the top 56 thereby contributing to a soft circulation of air which further assists in even heating or a room.

Referring to FIG. 9, a free-standing version is shown that can be placed on a floor using a floor stand 59. The unit is finished on both of its surfaces with a non-reflective coating 49. Radiant heat 55 is emitted in both directions. Some convection also contributes to the heating of a room.

It is widely known that radiant heat does not heat the air, but rather it heats the objects upon which the line-of sight radiant waves are absorbed. The economy of the invention is appreciated in contrast to the more common forced air heating such as central heating used in most homes in the United States. The comfort of a person in the presence of a radiant heater can be appreciated by the experience of dining at an outdoor café heated by the well-known butane radiant heater. The cool outside air would cause discomfort and chilling, were it not for the radiant heater overhead. Indoor radiant heating exhibits similar comfort, but at a lesser cost because energy is not used to heat the air in the room. In contrast to forced air heating, a radiantly heated room will feel as comfortable as a room at 72 degrees F. while the air temperature is actually 55 degrees F. With this invention the cost of energy required to raise the temperature of the air from 55 degrees F. to 72 degrees is the economic savings.

In summary, the purpose of the metal supports is to mount a heater with a surface or surfaces from which IR radiation is emitted, and also to provide an enclosure for the liquid and the electrodes. Preferably this is done by holding in place the bladder and its heating element. Instead the edges could be joined and water proof joinders could be provided, without a bladder, and this is within the scope of the invention. The material would be plastic coated to resist oxidation while the material of the bladder could be rigid and formed, it is best and most economical practice for it to be resilient which is one good reason to use a bladder. With the resiliency it can make good surface contact with the metal support and can readily convey its heat to the supports.

Also, the sheets forming the bladder can be joined at their edges. To form the channels the sheets can be fused together at appropriate places. Then channels for liquid to flow through will be formed between those places when the bladder is filled with liquid.

The heater element is placed at the bottom of the enclosure (if the bladder is a bladder used). Cooler water flows by convection downwardly to it. When heated, it rises and flows through the serpentine channels upwardly from lower center. When it cools, the water flows toward the sides and downward to the heater. The flow needs no pump. Internal convection is sufficient for the purpose.

The preferred liquid is water. It is possible, but rarely will be desired, to add different liquids to it, or to use other liquids instead of water. They are within the scope of this invention.

Also, an electrolyte is needed to provide necessary conductivity for the water. The most appropriate electrolyte is sodium chloride. It is cheap and its properties are well-known and are well-suited to this invention. Still, other electrolytes could instead be used, alone or along with the sodium chloride and still be within the scope of this invention. Salts of other metals, and ions other than chloride may be used if desired but would be a very unusual situation.

While the invention is shown as a flat body suitable for being placed against a wall or on a stand, it need not be flat or planar. Instead it could be bent, or even cylindrical or semi-cylindrical. The objective is to have an emitting surface facing into an area where infrared radiation is desired for heating, and a gross shape that enables convection flow.

The use of PPTC (polymeric positive temperature coefficient) material for the electrodes is central to this invention. The phenomenon of reduction or cut off of current (by increase of resistance) as a function of temperature is known, but not widely appreciated. Knowledgeable persons in the art can readily locate sources for these products. Intended properties for a specific application are given above. When the material is obtained, the appropriate concentration of electrolytes in the liquid will be experimentally determined. With a suitable conductivity in the liquid and appropriate cut-off temperature, the heater is ready to work.

There is no need for a circuit breaker or other device to respond to overheating. The system simply will not overheat, and merely stops drawing current when the temperature of the electrodes meets or exceeds the cut-off temperature. This can occur by the self-heating of the electrodes themselves by internal resistive heating, or by heating of the electrodes by the water, or by both. There are therefore two means by which the system will be shut down, both of which occur within the body of the electrodes.

This invention is not to be limited by the embodiments shown in the drawings and described in the description, which are given by way of example and not of limitation, but only in accordance with the scope of the appended claims. 

1. An infrared wavelength emitting heater comprising: an enclosure having a pair of spaced-apart opposite sides joined at their periphery to form an internal liquid-tight cavity, at least one of said sides including a surface from which infrared wavelength energy will be emitted as the consequence of the temperature of liquid in said cavity; an electrode assembly in said enclosure near the bottom and between said sides, said electrodes being spaced apart from one another, said electrodes being connectable to a source of electrical current; fluid-flow passages in said enclosure so disposed and arranged as to encourage liquid heated by said electrode assembly to rise toward the top and return downwardly along the sides to the electrode assembly; liquid in said enclosure having a known electrical resistance for joule heating by electrical current flowing through it between said electrodes; said electrodes being submersed in said liquid with said liquid between them, and comprising a polymeric material with a positive temperature coefficient such that at a known cut-off temperature of the electrodes, the resistance of the electrodes to current flow rises to materially reduce or to cut-off flow of electrical current through them, said cut-off temperature being attained in response to resistance heating of the electrodes themselves and of the temperature of the liquid in which it is submersed.
 2. A heater according to claim 1 in which said surface is constituted to emit said infrared energy.
 3. A heater according to claim 2 in which said surface is formed to be a front side and the other side is a second side opposite to it and formed of material not transmissive of infrared energy, whereby the major portion of infrared energy is emitted from said surface.
 4. A heater in which a liquid-tight bladder is fitted inside said enclosure to hold said liquid, with the electrodes disposed in the bladder, the bladder being in surface to surface contact with the inside of said sides.
 5. A heater according to claim 4 in which the bladder is substantially formed of resilient material, having a pair of opposite sides, said opposite sides being locally joined to provide said flow channels between them when the bladder filled with liquid.
 6. A heater according to claim 1 in which said electrodes are separated by insulation to provide said spacing in which liquid is to be heated.
 7. A heater according to claim 5 in which said electrodes are separated by insulation to provide said spacing in which liquid is to be heated.
 8. A heater according to claim 1 in which said liquid is water in which an electrolyte is dissolved in concentration known to produce an electrical resistance between said electrodes which enables the water to be joule heated to a temperature at least as high as the cut-off temperature.
 9. A heater according to claim 5 in which said electrolyte comprises sodium chloride.
 10. A heater according to claim 5 in which said liquid is water in which an electrolyte is dissolved in concentration known to produce an electrical resistance between said electrodes which enables the water to be joule heated to a temperature at least as high as the cut-off temperature.
 11. A heater according to claim 10 in which said electrolyte comprises sodium chloride.
 12. A heater according to claim 2 in which both sides include a said infrared wavelength energy emitting surface.
 13. A heater according to claim 12 in which a stand supports said heater, whereby it can be placed where infrared energy is desired from both sides.
 14. A heater according to claim 3 in which means is provided to mount the heater to a wall, said other side being reflective of said energy. 